314 GENERAL PLANT PATHOLOGY 



The final outcome of the disease may be a complete destruction of 

 the host (Fig. 127), or its complete recovery. The simplest cases are leaf 

 spots, or fruit spots, which are removed from the plant when the leaves 

 and fruits fall without in any way jeopardizing the general health of the 

 plant. Sometimes the plant recovers from bacterial, or fungal diseases, 

 but such recovery does not protect the plant from subsequent attacks 

 of the same disease, as is the case with some diseases of animals. Old 

 and slow-growing cabbages are rather resistant to Pseudomonas cam- 

 pestris while young and rapidly growing plants are apt to be destroyed. 

 Vaccination of plants to ward off diseases has never been successful, 

 and it is doubtful whether this means of protection is available for 

 plants. It is, however, a wholly unworked field. Some experiments 

 which Smith, Townsend and Brown performed in 1908 and 1909 seem 

 to show that after Paris daisies have been inoculated several times with 

 Pseudomonas tumefaciens with the production of tumors, that subse- 

 quent inoculations with cultures of the same virulence are without 

 effect, but owing to the possibility that the results were due to loss of 

 virulence, the experiments were inconclusive. For the student, who 

 may be interested in pursuing this line of important research work 

 further, the following bibliography is here given, taken from Smith. 



Shattock, Samuel G.: The Healing of Incisions in Vegetable Tissues. Journ. 



Path, and Bact. Edinburgh and London, v: 39-58, 1898. 

 HiLTNER, L. and Stormer, K.: Neue Untersuchungen iiber die WurzelknoUchen 



der Legurainosen und deren Erreger. Arb. a.d. Biologischen Abt. fur Land- 



und Forstwirthschaft am Kaiser. Gesundheitsamte iii, heft 3: 151, 1903. 

 Brullowa, J. P.: Ueber den Selbstschutz der Pflanzenzelle gegen Pilzinfektion. 



Jahrb. f. Pflz. Krh. K. Bot. Garten Petersb., Nr. 4, 1907. 

 Alten, H. von: Zur Thyllenfrage. Callusartige Wucherungen in verlezten 



Blattstielen von Nuphar luteum. Bot. Ztg., 68, part ii: 89-95, 1910. 

 Smith, Erwin F.: Bacteria in Relation to Plant Diseases, ii: 93-94, 1914. 



DISSEMINATION OF FUNGI 



Fungi are usually reproduced by spores, which are minute and light 

 and easily carried about by various agents, such as on seeds, by the wind, 

 by water, by insects, by other animals, by agricultural and commer- 

 cial practices and by railroads, cars and other vehicles. The black-leg, 

 or Phoma wilt of cabbage of recent introduction, was introduced from 

 Europe undoubtedly with imported seed, and as we have seen various 



